U.S. patent number 9,908,953 [Application Number 13/745,346] was granted by the patent office on 2018-03-06 for crosslinker-accelerator system for polyacrylates.
This patent grant is currently assigned to TESA SE. The grantee listed for this patent is tesa SE. Invention is credited to Sarah Bamberg, Jennifer Beschmann, Marten Papenbroock, Alexander Prenzel.
United States Patent |
9,908,953 |
Prenzel , et al. |
March 6, 2018 |
Crosslinker-accelerator system for polyacrylates
Abstract
Controlled thermal crosslinking in a polyacrylate-based
composition is accomplished by a crosslinker-accelerator system for
the thermal crosslinking of polyacrylates having functional groups
suitable for entering into linking reactions with epoxide groups,
comprising at least one substance comprising at least one epoxide
group (crosslinker) and at least one substance of the general
formula (I)
R.sup.1R.sup.2N--CR.sup.3R.sup.4--CR.sup.5R.sup.6--(CR.sup.7R.sup.8).sub.-
n--NR.sup.9R.sup.10 (I) wherein the radicals R.sup.1, R.sup.2,
R.sup.9 and R.sup.10 independently of one another are a hydrogen
atom or a substituted or unsubstituted alkyl or cycloalkyl radical
having 1 to 8 carbon atoms or an alkylene group bonded to the main
chain and having 1 to 8 carbon atoms, where at least one of the
radicals R.sup.1, R.sup.2, R.sup.9 and R.sup.10 is not a hydrogen
atom; the radicals R.sup.3, R.sup.4, R.sup.5, R.sup.6, R.sup.7 and
R.sup.8 independently of one another are a hydrogen atom or an
alkyl group having 1 to 8 carbon atoms or form a 5-7-membered
cycloalkylene group; and n is an integer from 0 to 4
(accelerator).
Inventors: |
Prenzel; Alexander (Hamburg,
DE), Bamberg; Sarah (Hamburg, DE),
Beschmann; Jennifer (Hamburg, DE), Papenbroock;
Marten (Hamburg, DE) |
Applicant: |
Name |
City |
State |
Country |
Type |
tesa SE |
Hamburg |
N/A |
DE |
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Assignee: |
TESA SE (Norderstedt,
DE)
|
Family
ID: |
47561337 |
Appl.
No.: |
13/745,346 |
Filed: |
January 18, 2013 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20130190457 A1 |
Jul 25, 2013 |
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Foreign Application Priority Data
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Jan 20, 2012 [DE] |
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10 2012 200 854 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C08F
20/18 (20130101); C09J 133/00 (20130101); C08K
5/17 (20130101); C08K 5/1515 (20130101) |
Current International
Class: |
C08F
20/18 (20060101); C08K 5/1515 (20060101); C08K
5/17 (20060101); C09J 133/12 (20060101); C09J
133/10 (20060101); C09J 133/00 (20060101); C09J
133/08 (20060101) |
Field of
Search: |
;525/330.5 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1576291 |
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Feb 2005 |
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CN |
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101679822 |
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Mar 2010 |
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CN |
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102004044086 |
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Mar 2006 |
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DE |
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0752435 |
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Jan 1997 |
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EP |
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13115555 |
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Mar 2005 |
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EP |
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1978069 |
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Oct 2008 |
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EP |
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200909485 |
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Mar 2009 |
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TW |
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2006027387 |
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Mar 2006 |
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WO |
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Other References
German Search Report for DE 102012200854.3 dated Jul. 25, 2012.
cited by applicant .
English language abstract for DE 102004044086 which published Mar.
16, 2006. cited by applicant .
"Influence of Diluent and of Copolymer Composition on the Glass
Temperature of a Polymer System", T. G. Fox, Rohm & Haas
Company, p. 123, 1956. cited by applicant .
"Communication: A Table of Fikentscher K Values versus Relative
Viscosities for a Concentration of 1.0", P. E. Hinkamp, Plastics
Production Research Service, p. 381-384, 1966. cited by applicant
.
European Search Report for EP 13150155.3 dated Apr. 23, 2013. cited
by applicant .
English language translation of Taiwanese Office Action and Search
Report for corresponding application TW 101149962 dated May 18,
2016. cited by applicant .
English translation of CN Office Action for corresponding CN
application 201310020997.2 dated Feb. 4, 2016. cited by applicant
.
English translation of CN Search Report for corresponding CN
application 201310020997.2 dated Jan. 27, 2016. cited by
applicant.
|
Primary Examiner: Choi; Ling Siu
Assistant Examiner: Nguyen; Thuy-Ai N
Attorney, Agent or Firm: Norris McLaughlin & Marcus
PA
Claims
The invention claimed is:
1. A pressure-sensitive adhesive composition adapted to be
crosslinked by a crosslinker-accelerator system which is effective
in the thermal crosslinking of polyacrylates having functional
groups suitable for entering into linking reactions with epoxide
groups, wherein the crosslinker-accelerator system comprises: a
crosslinker comprising at least one substance having at least one
epoxide group; and an accelerator having at least one compound
selected from: 3-(dimethylamino)-1-propylamine,
N,N'-dimethyl-1,3-propanediamine,
N,N,N'-trimethyl-1,3-propanediamine, N-methyl-1,3-diaminopropane,
N,N,2,2-tetramethyl-1,3-propane-diamine,
N,N',2-trimethyl-1,3-propanediamine,
(3-amino-2-methylpropyl)dimethylamine,
(1-ethyl-3-piperidinyl)methanamine,
N,N,N',N'',N''-penta-methyldipropylenetriamine,
N,N-bis(3-dimethylaminopropyl)-N-isopropanolamine,
N-(3-dimethylaminopropyl)-N,N-diisopropanolamine,
N'-(3-(dimethylamino)propyl)-N,N-dimethyl-1,3-propanediamine, and
N,N,N'-trimethylaminoethylethanolamine, and wherein the ratio of
the total number of epoxide groups in the crosslinker to the number
of functional groups in the polyacrylate that are suitable for
entering into linking reactions with epoxide groups is in the range
from 0.01:1 to 1:1.
2. The pressure-sensitive adhesive composition according to claim
1, wherein the crosslinker-accelerator system comprises
N'-(3-(dimethylamino)propyl)-N,N-dimethyl-1,3-propanediamine.
3. Method for the thermal crosslinking of polyacrylates having
functional groups suitable for entering into linking reactions with
epoxide groups, comprising the use of a crosslinker-accelerator
system according to claim 1.
4. The pressure sensitive adhesive composition according to claim
1, in which the accelerator has at least one compound selected
from: 3-(dimethylamino)-1-propylamine,
N,N'-dimethyl-1,3-propanediamine,
N,N,N'-trimethyl-1,3-propanediamine, N-methyl-1,3-diaminopropane,
N,N,2,2-tetramethyl-1,3-propane-diamine,
N,N',2-trimethyl-1,3-propanediamine,
(3-amino-2-methylpropyl)dimethylamine,
(1-ethyl-3-piperidinyl)methanamine,
N,N-bis(3-dimethylaminopropyl)-N-isopropanolamine,
N-(3-dimethylaminopropyl)-N,N-diisopropanolamine,
N'-(3-(dimethylamino)propyl)-N,N-dimethyl-1,3-propanediamine, and
N,N,N'-trimethylaminoethylethanolamine.
Description
The present invention relates to the technical field of
crosslinkable polyacrylates. In particular a system is proposed for
controlling the crosslinking rate of thermally crosslinkable
polyacrylates, this system being based on the combination of a
substance containing epoxide groups with at least one specific
diamine or polyamine.
Polyacrylates are widely used for high-grade industrial
applications, as adhesives, more particularly as pressure-sensitive
adhesives or heat-sealing adhesives, having proved to be highly
suitable for the growing requirements in these areas of
application. For instance, pressure-sensitive adhesives (PSAs) are
required to have a good initial tack, but also to meet exacting
requirements in terms of shear strength. At the same time these
compositions must be suitable for coating onto carrier materials.
All of this can be achieved through the use of polyacrylates with a
high molecular weight and high polarity, and their efficient
crosslinking. Moreover, polyacrylates can be produced to be
transparent and stable to weathering.
For the coating of polyacrylate compositions useful as PSA from
solution or as a dispersion, thermal crosslinking has long been
state of the art. In general, the thermal crosslinker--for example
a polyfunctional isocyanate, a metal chelate or a polyfunctional
epoxide--is added to the solution or dispersion of a polyacrylate
equipped with corresponding functional groups, the resulting
composition is coated as a sheetlike film onto a substrate, and the
coating is subsequently dried. Through this procedure, organic
solvents, or water in the case of dispersions, are evaporated, and
the polyacrylate, accordingly, is crosslinked. Crosslinking is very
important for the coatings, since it gives them sufficient cohesion
and thermal shear strength. Without crosslinking, the coatings
would be too soft and would flow away under even a low load.
Critical to a good coating outcome is the observance of the potlife
(processing life, within which the system is in a processible
state), which can vary greatly according to crosslinking system. If
this life is too short, the crosslinker has already undergone
reaction in the polyacrylate solution; the solution is already
partly crosslinked and can no longer be applied uniformly.
The technological operation for producing PSAs is in a state of
continual onward development. Motivated by more restrictive
environmental impositions and by rising prices for solvents, an aim
is to eliminate the solvents as far as possible from the
manufacturing operation. Within the industry, therefore, there is
continual growth in the importance of melt processes (also referred
to as hotmelt processes) with solvent-free coating technology for
the production of PSAs. In such processes, meltable polymer
compositions, i.e. polymer compositions which at elevated
temperatures enter into the fluid state without decomposing, are
processed. Such compositions can be processed outstandingly from
the melt state. In ongoing developments of this procedure, an aim
is to make the production of the product compositions as well a
low-solvent or solvent-free operation.
The introduction of the hotmelt technology is imposing growing
requirements on the adhesives. Meltable polyacrylate compositions
in particular (synonymous designations: "polyacrylate hotmelts",
"acrylate hotmelts") are being investigated very intensively for
improvements. In the coating of polyacrylate compositions from the
melt, thermal crosslinking has to date not been very widespread, in
spite of the potential advantages of this method.
Acrylate hotmelts have to date been crosslinked primarily through
radiation-chemical methods (UV irradiation, EBC irradiation). This
procedure, however, is associated with a variety of disadvantages:
In the case of crosslinking by means of UV rays, only
UV-transparent (UV-pervious) layers can be crosslinked. In the case
of crosslinking with electron beams (electron beam crosslinking or
electron beam curing, also EBC), the electron beams possess only a
limited depth of penetration, which is dependent on the density of
the irradiated material and on the accelerator voltage. In both of
the aforementioned methods, the layers after crosslinking have a
crosslinking profile, and the pressure-sensitive adhesive layer
does not crosslink homogeneously.
The pressure-sensitive adhesive layer must be relatively thin in
order for well-crosslinked layers to be obtainable by chemical
radiation methods. The thickness through which radiation can pass,
though indeed varying as a function of density, accelerator voltage
(EBC) and/or active wavelength (UV), is always greatly limited;
accordingly, it is not possible to effect crosslinking through
layers of arbitrary thickness, and certainly not homogeneously.
Also known in the prior art are a number of processes for the
thermal crosslinking of acrylate hotmelts. In each of these
processes a crosslinker is added to the acrylate melt prior to
coating, and then the composition is shaped and wound to form a
roll.
Direct thermal crosslinking of acrylate hotmelt compositions
comprising NCO-reactive groups is described in EP 0 752 435 A1. The
isocyanates used, which are free from blocking agents and are, more
particularly, sterically hindered and dimerised isocyanates,
require very drastic crosslinking conditions, and so a rational
technical implementation presents problems. Under the kind of
conditions which prevail on processing from the melt, the procedure
described in EP 0 752 435 A1 leads to rapid and relatively
extensive crosslinking, and so coating of the composition onto
carrier materials is difficult. In particular it is not possible to
obtain homogeneous layers of adhesive of the kind that are needed
for many technical applications of adhesive tapes.
Also prior art is the use of blocked isocyanates. A disadvantage of
this approach is the release of blocking groups or fragments which
may have an adverse effect on the technical adhesive properties.
One example is U.S. Pat. No. 4,524,104 A. It describes
pressure-sensitive acrylate hotmelt adhesives which can be
crosslinked using blocked polyisocyanates together with
cycloamidines or salts thereof as catalyst. With this system, the
required catalyst, but especially substances produced such as HCN,
phenol, caprolactam or the like, may severely impair the product
properties. With this approach, moreover, there is a need often for
drastic conditions in order to release the reactive groups.
Significant application of this approach is so far unknown and
appears, furthermore, to be unattractive.
DE 10 2004 044 086 A1 describes a process for the thermal
crosslinking of acrylate hotmelts that coats a solvent-free
functionalized acrylate copolymer, which following metered addition
of a thermally reactive crosslinker has a processing life that is
long enough for compounding, conveying and coating, onto a web-form
layer of a further material and then crosslinks this coating under
mild conditions until the cohesion achieved is sufficient for
pressure-sensitive adhesive tapes. A disadvantage of this process
is that the reactivity of the crosslinker (isocyanate)
predetermines the free processing life and the degree of
crosslinking. Isocyanate crosslinkers react in some cases even
during their addition; consequently, depending on the system, the
gel-free time can be very short. A composition with a sizable
fraction of functional groups such as hydroxyl groups or carboxylic
acid can in that case no longer be applied sufficiently well. A
streaky coat interspersed with gel specks and hence inhomogeneous
would be the result. Another problem which arises is that the
achievable degree of crosslinking is limited. If a higher degree of
crosslinking through addition of a higher quantity of crosslinker
is desired, this has disadvantages when polyfunctional isocyanates
are used. The composition would react too quickly and would be
coatable, if at all, only with a very short processing life and
hence at very high coating speeds, which would exacerbate the
problems of the non-homogeneous coating appearance.
Crosslinking by means of polyfunctional epoxides is described in EP
1 978 069 A1, it having been shown that through the use of
accelerators, without which the epoxides would undergo, to all
intents and purposes, no reaction with the carboxyl groups present
in the polymer, the degree of crosslinking can be adjusted
independently of the crosslinking kinetics. In order to make sure
that the composition is coatable after melt processing,
crosslinking in the extruder must take place only to a small extent
and must subsequently continue at temperatures lower than in the
extruder, in order for ideal product properties to be achieved.
While the crosslinker-accelerator systems described in EP 1 978 069
A1 do meet this requirement and can be used industrially, the
secondary crosslinking at room temperature was too slow. Secondary
crosslinking at elevated temperatures is frequently undesirable if
the PSAs have already been wound up into rolls, which may lose
their shape as a result of the heat-treatment steps.
Epoxides react fundamentally only under the influence of heat, and
more particularly only after prolonged supply of thermal energy.
Known accelerator substances such as ZnCl.sub.2, for example, do
lead to an improvement in the reaction capacity within the
temperature range of polymer melts, but in the absence of a supply
of thermal energy from the outside (in other words, for example, at
room temperature), the reactivity of the epoxides is lost, even in
the presence of the accelerators, and so the crosslinking reaction
breaks down (in other words, at the prevailing temperature, the
accelerators no longer have an accelerating activity). This is a
problem especially when the polyacrylates processed as a hotmelt
are coated within relatively short time periods (several minutes)
and then, in the absence of a further supply of heat, cooled
rapidly down to room temperature or storage temperature. Without
initiation of a further crosslinking reaction it would not be
possible to achieve high degrees of crosslinking, and for numerous
fields of application of polyacrylates, such as their use as PSAs
in particular, this would have the very deleterious consequence of
inadequate cohesion of the composition.
If the crosslinker system, with only thermally functioning
accelerators, such as ZnCl.sub.2, were to be introduced too early
into the polyacrylate system (in order to achieve a sufficient
degree of crosslinking), then the compositions would no longer be
able to be homogeneously processed, more particularly compounded
and coated, since they would crosslink too quickly or would even
"gel" (undergo uncontrolled crosslinking). If, on the other hand,
the accelerator causes too little activation of epoxide
crosslinking, then a very long secondary crosslinking time can be
expected or the compositions will have to be stored at high
temperatures, which is undesirable.
It is an object of the present invention to enable thermal
crosslinking of polyacrylate compositions which can be processed
from the melt ("polacrylate hotmelts"), the intention being that
there should be a sufficiently long processing life ("potlife")
available for processing from the melt, especially as compared with
the potlife in the case of the known thermal crosslinking systems
for polyacrylate hotmelts. It ought at the same time to be possible
to do without the use of protective groups, which would have to be
removed again possibly by actinic radiation or other methods.
Moreover, the intention is that it should be possible to set the
degree of crosslinking of the polyacrylate composition to a desired
level, without adversely affecting the advantages of the operating
regime. Even at low temperatures, the secondary crosslinking is to
proceed rapidly to an end level.
In the text below, the polyacrylate compositions are also referred
to synonymously for short as "polyacrylates". For the
noncrosslinked polyacrylate compositions, the term "polymerisates"
is also used, while the term "polymers" is used for the fully or
partly crosslinked polyacrylate compositions.
The above object is achieved by means of a specific
crosslinker-accelerator system comprising at least one epoxide
compound and at least one specific diamine or polyamine. A first
subject of the invention, therefore, is a crosslinker-accelerator
system for the thermal crosslinking of polyacrylates having
functional groups suitable for entering into linking reactions with
epoxide groups, comprising
at least one substance comprising at least one epoxide group
(crosslinker) and
at least one substance conforming to the general formula (I)
R.sup.1R.sup.2N--CR.sup.3R.sup.4--CR.sup.5R.sup.6--(CR.sup.7R.sup.8).sub.-
n--NR.sup.9R.sup.10 (I) in which the radicals R.sup.1, R.sup.2,
R.sup.9 and R.sup.10 independently of one another are a hydrogen
atom or a substituted or unsubstituted alkyl or cycloalkyl radical
having 1 to 8 carbon atoms or an alkylene group bonded to the main
chain and having 1 to 8 carbon atoms, where at least one of the
radicals R.sup.1, R.sup.2, R.sup.9 and R.sup.10 is not a hydrogen
atom; the radicals R.sup.3, R.sup.4, R.sup.5, R.sup.6, R.sup.7 and
R.sup.8 independently of one another are a hydrogen atom or an
alkyl group having 1 to 8 carbon atoms or form a 5-7-membered
cycloalkylene group; and n is an integer from 0 to 4
(accelerator).
A crosslinker-accelerator system of this kind enables, initially,
comfortable processing lives for the polyacrylate compositions,
while later a speedy secondary crosslinking is ensured even at low
temperatures, more particularly at room temperature. The
crosslinker-accelerator system of the invention avoids the
above-recited disadvantages of conventional crosslinking systems,
and is custom-tailored to the requirements of an industrially
implemented operation for producing PSAs or PSA-coated
products.
As a result of the inventive combination of the stated components
it is possible to offer a thermal crosslinking process which when
applied to the processing of polyacrylate hotmelt compositions does
not lead to uncontrolled reactions (gelling of the composition) and
leaves a sufficiently long time for processing (potlife), thus
making it possible in particular to achieve a uniform and
blister-free coating when the composition is coated out as a layer
or is applied to a carrier. A very advantageous effect of the
crosslinker-accelerator system of the invention is that the
necessary secondary crosslinking of the polyacrylate composition
after processing, more particularly after being coated out as a
layer or applied to a carrier, proceeds rapidly, with a supply of
thermal energy reduced significantly by comparison with melt
production, in other words after cooling, without any need for
actinic irradiation for this purpose. By rapid crosslinking is
meant that the elastic fraction of the composition, measured by
means of microshear travel method H3, is significantly more than
25%, more preferably more than 35%, within a week.
As a result of the crosslinker-accelerator system of the invention,
the polyacrylates are capable of undergoing further crosslinking
without further thermal energy (heating) supplied actively--that
is, by technical process means--more particularly after cooling to
room temperature (RT, 20.degree. C.) or to a temperature close to
room temperature. More particularly it is possible in this
crosslinking phase to do without heating, without this leading to a
termination of the crosslinking reaction.
A "crosslinker" for the purposes of the invention is a substance
via which the polyacrylate molecules are linked to form
three-dimensional structures by formation of covalent bonds. An
"accelerator" is a substance which supports the crosslinking
reaction by ensuring a significantly increased crosslinking
reaction rate in comparison to the absence of the accelerator. This
is true, of course, in the case of comparable reaction parameters
and more particularly at temperatures below the melting temperature
of the polyacrylates. Within this temperature range, the
crosslinking reaction without accelerators would not proceed at all
or would proceed only very slowly. The accelerator, then, produces
a substantial improvement in the reaction kinetics of the
crosslinking reaction. In accordance with the invention this can be
done catalytically, but also by incorporation into the reaction
event.
"Polyacrylates" are polymers whose monomer basis, in terms of
amount of substance, consists to an extent of at least 30% of
acrylic acid, methacrylic acid, acrylic esters and/or methacrylic
esters, with acrylic esters and/or methacrylic esters being present
at least proportionally, generally and preferably to an extent of
at least 30%. More particularly, a "polyacrylate" is a polymerisate
which is obtainable by radical polymerization of acrylic and/or
methylacrylic monomers and also, optionally, further,
copolymerisable monomers.
The crosslinker-accelerator system of the invention comprises at
least one substance which contains at least one epoxide group as
crosslinker. Substances containing epoxide groups that are used are
preferably polyfunctional epoxides, these being those which have at
least two epoxide functions per molecule (i.e. are at least
difunctional in respect of the epoxide groups). They may be either
aromatic or aliphatic compounds.
Examples of suitable polyfunctional epoxides are oligomers of
epichlorohydrin, epoxy ethers of polyhydric alcohols (more
particularly ethylene, propylene and butylene glycols, polyglycols,
thiodiglycols, glycerol, pentaerythritol, sorbitol, polyvinyl
alcohol, polyallyl alcohol and the like); epoxy ethers of
polyhydric phenols (more particularly resorcinol, hydroquinone,
bis(4-hydroxyphenyl)methane, bis(4-hydroxy-3-methylphenyl)methane,
bis(4-hydroxy-3,5-dibromophenyl)methane,
bis(4-hydroxy-3,5-difluorophenyl)methane,
1,1-bis(4-hydroxyphenyl)ethane, 2,2-bis(4-hydroxyphenyl)propane,
2,2-bis(4-hydroxy-3-methylphenyl)propane,
2,2-bis(4-hydroxy-3-chlorophenyl)propane,
2,2-bis(4-hydroxy-3,5-dichlorophenyl)propane,
2,2-bis(4-hydroxy-3,5-dichlorophenyl)propane,
bis(4-hydroxyphenyl)phenylmethane,
bis(4-hydroxyphenyl)diphenylmethane,
bis(4-hydroxyphenyl)-4'-methylphenylmethane,
1,1-bis(4-hydroxyphenyl)-2,2,2-trichloroethane,
bis(4-hydroxyphenyl)-(4-chlorophenyl)methane,
1,1-bis(4-hydroxyphenyl)cyclohexane,
bis(4-hydroxyphenyl)cyclohexylmethane, 4,4'-dihydroxybiphenyl,
2,2'-dihydroxybiphenyl, 4,4'-dihydroxydiphenyl sulphone) and also
their hydroxyethyl ethers; phenol-formaldehyde condensation
products such as phenol alcohols, phenol aldehyde resins and the
like; S- and N-containing epoxides (for example
N,N-diglycidylaniline,
N,N'-dimethyldiglycidyl-4,4-diaminodiphenylmethane) and also
epoxides prepared by customary methods from polyunsaturated
carboxylic acids or monounsaturated carboxylic esters of
unsaturated alcohols, glycidyl esters, polyglycidyl esters, which
may be obtained by polymerization or copolymerization of glycidyl
esters of unsaturated acids, or are obtainable from other acidic
compounds (cyanuric acid, diglycidyl sulphide, cyclic trimethylene
trisulphone and/or derivatives thereof, and others).
Examples of ethers containing epoxide groups that are very suitable
in accordance with the invention include 1,4-butanediol diglycidyl
ether, polyglycerol-3 glycidyl ether, cyclohexanedimethanol
diglycidyl ether, glycerol triglycidyl ether, neopentyl glycol
diglycidyl ether, pentaerythritol tetraglycidyl ether,
1,6-hexanediol diglycidyl ether, polypropylene glycol diglycidyl
ether, trimethylolpropane triglycidyl ether, bisphenol A diglycidyl
ether and bisphenol F diglycidyl ether.
The crosslinker-accelerator system of the invention further
comprises at least one substance conforming to the general formula
(I)
R.sup.1R.sup.2N--CR.sup.3R.sup.4--CR.sup.5R.sup.6--(CR.sup.7R.sup.8).sub.-
n--NR.sup.9R.sup.10 (I) in which the radicals R.sup.1, R.sup.2,
R.sup.9 and R.sup.10 independently of one another are a hydrogen
atom or a substituted or unsubstituted alkyl or cycloalkyl radical
having 1 to 8 carbon atoms or an alkylene group bonded to the main
chain and having 1 to 8 carbon atoms, where at least one of the
radicals R.sup.1, R.sup.2, R.sup.9 and R.sup.10 is not a hydrogen
atom; the radicals R.sup.3, R.sup.4, R.sup.5, R.sup.6, R.sup.7 and
R.sup.8 independently of one another are a hydrogen atom or an
alkyl group having 1 to 8 carbon atoms or form a 5-7-membered
cycloalkylene group; and n is an integer from 0 to 4, as
accelerator.
By "substituted" is meant that a hydrogen atom which is bonded to a
carbon atom belonging to the respective radical is replaced by
another atom or by a chemical group, such as a functional group,
for example, where the group atom bonded directly to the relevant
carbon atom of the radical may in particular also be a heteroatom,
in other words not a carbon atom. The term "substituted alkyl
radical" covers radicals which in spite of substitution can still
be identified as alkyl radicals in terms of their essential nature.
These include, for example, radicals that are halogenated in
position 1, in other words on the carbon atom bonded directly to
the nitrogen atom. Not covered by the term "substituted alkyl
radical", in contrast, are radicals, for example, whose carbon atom
in position 1 is part of a carbonyl group or of a comparable
functional group, which no longer allows the radical in question to
be classed, in terms of its essential nature, among the alkyl
radicals.
"Alkylene group bonded to the main chain" means that the alkylene
group in question joins the nitrogen atom to one of those carbon
atoms to which the radicals R.sup.3 to R.sup.8 belong.
Suitable substances corresponding to the general formula (I) are,
for example, 3-(dimethylamino)-1-propylamine,
N,N'-dimethyl-1,3-propanediamine,
N,N,N'-trimethyl-1,3-propanediamine, N-methyl-1,3-diaminopropane,
N,N,2,2-tetramethyl-1,3-propane-diamine,
N,N',2-trimethyl-1,3-propanediamine,
(3-Amino-2-methylpropyl)dimethylamine,
(1-ethyl-3-piperidinyl)methanamine, pentamethyldiethylenetriamine
N,N,N',N'',N''-penta-methyldipropylenetriamine,
N,N-bis(3-dimethylaminopropyl)-N-isopropanolamine,
N-(3-dimethylaminopropyl)-N,N-diisopropanolamine,
N'-(3-(dimethylamino)propyl)-N,N-dimethyl-1,3-propanediamine,
N,N,N'-trimethylaminoethylethanolamine. The substance corresponding
to the general formula (I) is preferably selected from the
substances listed above.
Preferably, at least one of the radicals R.sup.1, R.sup.2, R.sup.9
and R.sup.10 in the general formula (I) is a methyl group. More
preferably, R.sup.1 and R.sup.2 and/or R.sup.9 and R.sup.10 are
each a methyl group. This means that either both R.sup.1 and
R.sup.2 or both R.sup.9 and R.sup.10 or all radicals R.sup.1,
R.sup.2, R.sup.9 and R.sup.10 in the general formula (I) are a
methyl group.
The radicals R.sup.1, R.sup.2, R.sup.9 and R.sup.10 in the general
formula (I) may additionally be, as substituted alkyl radicals, for
example, aminoalkyl groups or hydroxyalkyl groups. A radical
R.sup.1, R.sup.2, R.sup.9 and R.sup.10 in the form of an alkylene
group bonded to the main chain is found, for example, in
(1-ethyl-3-piperidinyl)methanamine.
It has additionally been found that a particularly positive effect
on the activity of the accelerator is achieved when two amine
functionalities are bonded to one another via a C.sub.2 bridge.
Preferably, therefore, n in the general formula (I) is 0
(zero).
More preferably, n in the general formula (I) is 0 (zero) and
R.sup.1 and R.sup.2 and/or R.sup.9 and R.sup.10 are each a methyl
group.
The at least one substance corresponding to the general formula (I)
is, preferably in accordance with the invention, selected from
N,N,N,N,N-pentamethyldiethylenetriamine and
N'-(3-(dimethylamino)propyl)-N,N-dimethyl-1,3-propanediamine. These
substances enable particularly efficient activation of bond
formation via the epoxide groups of the crosslinker.
A further subject of the present invention is a thermally
crosslinkable composition which comprises at least one polyacrylate
having functional groups suitable for entering into linking
reactions with epoxide groups, and a crosslinker-accelerator system
of the invention. This is more particularly a thermally
crosslinkable composition which comprises at least one polyacrylate
having functional groups which are suitable for entering into
linking reactions of epoxide groups,
at least one substance which comprises at least one epoxide group
(crosslinker), and
also at least one substance conforming to the general formula (I)
R.sup.1R.sup.2N--CR.sup.3R.sup.4--CR.sup.5R.sup.6--(CR.sup.7R.sup.8).sub.-
n--NR.sup.9R.sup.10 (I), in which the radicals R.sup.1, R.sup.2,
R.sup.9 and R.sup.10 independently of one another are a hydrogen
atom or a substituted or unsubstituted alkyl or cycloalkyl radical
having 1 to 8 carbon atoms or an alkylene group bonded to the main
chain and having 1 to 8 carbon atoms, where at least one of the
radicals R.sup.1, R.sup.2, R.sup.9 and R.sup.10 is not a hydrogen
atom; the radicals R.sup.3, R.sup.4, R.sup.5, R.sup.6, R.sup.7 and
R.sup.8 independently of one another are a hydrogen atom or an
alkyl group having 1 to 8 carbon atoms or form a 5-7-membered
cycloalkylene group; and n is an integer from 0 to 4
(accelerator).
The total fraction of substances which comprise at least one
epoxide group (crosslinkers) is preferably 0.1%-5% by weight, more
preferably 0.15%-0.4% by weight, based on the pure (without
additives) polyacrylate to be crosslinked. The total fraction of
accelerator is preferably 0.05%-5% by weight, more preferably
0.1%-1.2% by weight, based on the additive-free polyacrylate to be
crosslinked. "Pure polyacrylate to be crosslinked" means in
accordance with the invention "only the polyacrylate to be
crosslinked, without any additives". It is particularly
advantageous if the crosslinker fraction is selected so as to
result in an elastic fraction of the crosslinked polyacrylates of
at least 20%. The elastic fraction is preferably at least 40%, more
preferably at least 60% (measured in each case by measurement
method H3; cf. Experimental Section).
As monomers or comonomers for preparing the polyacrylate it is
preferred, accordingly, to make proportional use of functional
monomers which are crosslinkable with epoxide groups. These are
preferably monomers with acid groups (particularly carboxylic acid,
sulphonic acid or phosphonic acid groups) and/or hydroxyl groups
and/or acid anhydride groups and/or epoxide groups and/or amine
groups; monomers containing carboxylic acid groups are particularly
preferred. It is especially advantageous if the polyacrylate
comprises copolymerized acrylic acid and/or methacrylic acid.
Further monomers which may be used as comonomers for the
polyacrylate, besides acrylic and/or methacrylic esters having up
to 30 C atoms, are, for example, vinyl esters of carboxylic acids
comprising up to 20 C atoms, vinylaromatics having up to 20 C
atoms, ethylenically unsaturated nitriles, vinyl halides, vinyl
ethers of alcohols comprising 1 to 10 C atoms, aliphatic
hydrocarbons having 2 to 8 C atoms and 1 or 2 double bonds, or
mixtures of these monomers.
The properties of the polyacrylate (pressure-sensitive adhesive;
heat-sealing composition, viscoelastic non-tacky material and the
like) may be influenced in particular by varying the glass
transition temperature of the polymer, by means of different weight
fractions of the individual monomers.
For purely crystalline systems there is a thermal equilibrium
between crystal and liquid at the melting point T.sub.m. Amorphous
or semi-crystalline systems, in contrast, are characterized by the
transformation of the more or less hard amorphous or
semi-crystalline phase into a softer (rubberlike to viscous) phase.
At the glass point, particularly in the case of polymeric systems,
there is a "thawing" (or "freezing" in the case of cooling) of the
Brownian molecular motion of relatively long chain segments.
The transition from the melting point T.sub.m (also "melting
temperature"; really defined only for purely crystalline systems;
"polymer crystals") to the glass transition point T.sub.g (also
"glass transition temperature", "glass temperature") can therefore
be considered to be a fluid transition, depending on the proportion
of semi-crystallinity in the sample under analysis.
In the sense of the remarks above, when the glass transition point
is stated, the reference for the purposes of this specification
includes the melting point as well--in other words, the glass
transition point (or else, synonymously, the glass transition
temperature) is also understood to include the melting point for
the corresponding "melting" systems. The statements of the glass
transition temperatures relate to the determination by means of
dynamic mechanical analysis (DMA) at low frequencies.
In order to obtain polymers, as for example pressure-sensitive
adhesives or heat-sealing compositions, having desired glass
transition temperatures, the quantitative composition of the
monomer mixture is advantageously selected such that, in accordance
with an equation (E1) in analogy to the Fox equation (cf. T. G.
Fox, Bull. Am. Phys. Soc. 1956, 1, 123), the desired T.sub.g value
for the polymer is produced.
.times..times..times..times. ##EQU00001##
In this equation, n represents the serial number of the monomers
used, w.sub.n represents the mass fraction of the respective
monomer n (% by weight), and T.sub.g,n represents the respective
glass transition temperature of the homopolymer of each of the
monomers n, in K.
It is preferred to use a polyacrylate which can be traced back to
the following monomer composition: a) acrylic and/or methacrylic
esters of the following formula
CH.sub.2.dbd.C(R.sup.I)(COOR.sup.II) where R.sup.I.dbd.H or
CH.sub.3 and R.sup.II is an alkyl radical having 4 to 14 C atoms,
b) olefinically unsaturated monomers having functional groups of
the type already defined for reactivity with epoxide groups, c)
optionally further acrylates and/or methacrylates and/or
olefinically unsaturated monomers which are copolymerizable with
component (a).
For the use of the polyacrylate as a PSA, the fractions of the
corresponding components (a), (b) and (c) are selected such that
the polymerization product more particularly has a glass transition
temperature .ltoreq.15.degree. C. (DMA at low frequencies).
Especially for the preparation of PSAs it is very advantageous to
select the monomers of component (a) with a fraction from 45% to
99% by weight, the monomers of component (b) with a fraction from
1% to 15% by weight and the monomers of component (c) with a
fraction from 0% to 40% by weight (the figures are based on the
monomer mixture for the "base polymer", i.e. without additions of
any additives to the completed polymer, such as resins etc.).
For the use of the polyacrylate as a hotmelt adhesive, in other
words as a material which acquires its pressure-sensitive tack only
by virtue of heating, the fractions of components (a), (b), and (c)
are selected more particularly such that the copolymer has a glass
transition temperature (T.sub.g) of between 15.degree. C. and
100.degree. C., preferably between 30.degree. C. and 80.degree. C.,
more preferably between 40.degree. C. and 60.degree. C.
A viscoelastic material, which may typically be laminated on both
sides with pressure-sensitive adhesive layers, has a glass
transition temperature (T.sub.g) in particular of between
-50.degree. C. to +100.degree. C., preferably between -20.degree.
C. to +60.degree. C., more preferably 0.degree. C. to 40.degree. C.
Here again, the fractions of components (a), (b) and (c) should be
selected accordingly.
The monomers of component (a) are, in particular, plasticizing
and/or apolar monomers. As monomers (a) it is preferred to use
acrylic and methacrylic esters with alkyl groups consisting of 4 to
14 C atoms, more preferably 4 to 9 C atoms. Examples of monomers of
this kind are n-butyl acrylate, n-butyl methacrylate, n-pentyl
acrylate, n-pentyl methacrylate, n-amyl acrylate, n-hexyl acrylate,
hexyl methacrylate, n-heptyl acrylate, n-octyl acrylate, n-octyl
methacrylate, n-nonyl acrylate, isobutyl acrylate, isooctyl
acrylate, isooctyl methacrylate, and their branched isomers, such
as 2-ethylhexyl acrylate or 2-ethylhexyl methacrylate, for
example.
The monomers of component (b) are, in particular, olefinically
unsaturated monomers having functional groups, in particular having
functional groups which are able to enter into a reaction with the
epoxide groups.
Preference for component (b) is given to using monomers having
functional groups which are selected from the group encompassing:
hydroxyl, carboxyl, sulphonic acid or phosphonic acid groups, acid
anhydrides, epoxides, amines.
Particularly preferred examples of monomers of component (b) are
acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric
acid, crotonic acid, aconitic acid, dimethylacrylic acid,
.beta.-acryloyloxypropionic acid, trichloroacrylic acid,
vinylacetic acid, vinylphosphonic acid, itaconic acid, maleic
anhydride, hydroxyethyl acrylate, hydroxypropyl acrylate,
hydroxyethyl methacrylate, hydroxypropyl methacrylate,
6-hydroxyhexyl methacrylate, allyl alcohol, glycidyl acrylate,
glycidyl methacrylate.
As component (c) it is possible in principle to use all compounds
with vinylic functionalization which are copolymerizable with
component (a) and/or component (b). The monomers of component (c)
can serve to adjust the properties of the resultant PSA.
Monomers by way of example for component (c) are as follows:
methyl acrylate, ethyl acrylate, propyl acrylate, methyl
methacrylate, ethyl methacrylate, benzyl acrylate, benzyl
methacrylate, sec-butyl acrylate, tert-butyl acrylate, phenyl
acrylate, phenyl methacrylate, isobornyl acrylate, isobornyl
methacrylate, tert-butylphenyl acrylate, tert-butylphenyl
methacrylate, dodecyl methacrylate, isodecyl acrylate, lauryl
acrylate, n-undecyl acrylate, stearyl acrylate, tridecyl acrylate,
behenyl acrylate, cyclohexyl methacrylate, cyclopentyl
methacrylate, phenoxyethyl acrylate, phenoxyethyl methacrylate,
2-butoxyethyl methacrylate, 2-butoxyethyl acrylate,
3,3,5-trimethylcyclo-hexyl acrylate, 3,5-dimethyladamantyl
acrylate, 4-cumylphenyl methacrylate, cyanoethyl acrylate,
cyanoethyl methacrylate, 4-biphenyl acrylate, 4-biphenyl
methacrylate, 2-naphthyl acrylate, 2-naphthyl methacrylate,
tetrahydrofurfuryl acrylate, diethylaminoethyl acrylate,
diethylaminoethyl methacrylate, dimethylaminoethyl acrylate,
dimethylaminoethyl methacrylate, 2-butoxyethyl acrylate,
2-butoxyethyl methacrylate, methyl 3-methoxyacrylate,
3-methoxybutyl acrylate, phenoxyethyl acrylate, phenoxyethyl
methacrylate, 2-phenoxyethyl methacrylate, butyldiglycol
methacrylate, ethylene glycol acrylate, ethylene glycol
monomethylacrylate, methoxy polyethylene glycol methacrylate 350,
methoxy polyethylene glycol methacrylate 500, propylene glycol
monomethacrylate, butoxydiethylene glycol methacrylate,
ethoxytriethylene glycol methacrylate, octafluoropentyl acrylate,
octafluoropentyl methacrylate, 2,2,2-trifluoroethyl methacrylate,
1,1,1,3,3,3-hexafluoroisopropyl acrylate,
1,1,1,3,3,3-hexafluoroisopropyl methacrylate,
2,2,3,3,3-pentafluoropropyl methacrylate,
2,2,3,4,4,4-hexafluorobutyl methacrylate,
2,2,3,3,4,4,4-heptafluorobutyl acrylate,
2,2,3,3,4,4,4-heptafluorobutyl methacrylate,
2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluorooctyl methacrylate,
dimethylaminopropyl-acrylamide, dimethylaminopropylmethacrylamide,
N-(1-methylundecyl)acrylamide, N-(n-butoxymethyl)acrylamide,
N-(butoxymethyl)methacrylamide, N-(ethoxymethyl)-acrylamide,
N-(n-octadecyl)acrylamide, and also N,N-dialkyl-substituted amides,
such as, for example, N,N-dimethylacrylamide,
N,N-dimethylmethacrylamide, N-benzylacrylamide,
N-isopropylacrylamide, N-tert-butylacrylamide,
N-tert-octylacrylamide, N-methylolacryl-amide,
N-methylolmethacrylamide, acrylonitrile, methacrylonitrile, vinyl
ethers, such as vinyl methyl ether, ethyl vinyl ether, vinyl
isobutyl ether, vinyl esters, such as vinyl acetate, vinyl
chloride, vinyl halides, vinylidene chloride, vinylidene halides,
vinylpyridine, 4-vinylpyridine, N-vinylphthalimide, N-vinyllactam,
N-vinylpyrrolidone, styrene, .alpha.- and p-methylstyrene,
.alpha.-butylstyrene, 4-n-butylstyrene, 4-n-decylstyrene,
3,4-dimethoxystyrene, macromonomers such as 2-polystyrene-ethyl
methacrylate (molecular weight Mw from 4000 to 13 000 g/mol),
poly(methyl methacrylate)ethyl methacrylate (Mw from 2000 to 8000
g/mol).
Monomers of component (c) may advantageously also be selected such
that they contain functional groups which support subsequent
radiation-chemical crosslinking (by electron beams, UV, for
example). Suitable copolymerizable photoinitiators are, for
example, benzoin acrylate and acrylate-functionalized benzophenone
derivatives. Monomers which support crosslinking by electron
irradiation are, for example, tetrahydrofurfuryl acrylate,
N-tert-butylacrylamide, and allyl acrylate.
The polyacrylates may be prepared by processes familiar to the
skilled person, with particular advantage by conventional radical
polymerizations or controlled free-radical polymerizations. The
polyacrylates may be prepared by copolymerization of the monomeric
components using the usual polymerization initiators and also,
where appropriate, regulators (chain transfer agents), with
polymerization taking place at the customary temperatures in bulk,
in emulsion, such as in water or liquid hydrocarbons, for example,
or in solution.
The polyacrylates are prepared preferably by polymerization of the
monomers in solvents, more particularly in solvents with a boiling
range from 50 to 150.degree. C., preferably from 60 to 120.degree.
C., using the customary amounts of polymerization initiators, these
generally being 0.01% to 5%, more particularly 0.1% to 2%, by
weight (based on the total weight of the monomers).
Suitable in principle are all customary initiators that are
familiar to the skilled person. Examples of free-radical sources
are peroxides, hydroperoxides, and azo compounds, e.g., dibenzoyl
peroxide, cumene hydroperoxide, cyclohexanone peroxide,
di-tert-butyl peroxide, cyclohexylsulphonyl acetyl peroxide,
diisopropyl percarbonate, tert-butyl peroctoate, benzopinacol. In
one very preferred procedure, use is made as radical initiator of
2,2'-azobis(2-methylbutyronitrile) (Vazo.RTM. 67.TM. from DuPont)
or 2,2'-azobis-(2-methylpropionitrile)
(2,2'-azobisisobutyronitrile; AIBN; Vazo.RTM. 64.TM. from
DuPont).
Solvents contemplated include alcohols such as methanol, ethanol,
n- and iso-propanol, n- and iso-butanol, preferably isopropanol
and/or isobutanol; and also hydrocarbons such as toluene and, in
particular, benzines with a boiling range from 60 to 120.degree. C.
It is possible as well to use ketones such as, preferably, acetone,
methyl ethyl ketone, methyl isobutyl ketone, and esters such as
ethyl acetate, and also mixtures of solvents of the stated type,
with preference going to mixtures containing isopropanol,
particularly in amounts of 2% to 15% by weight, preferably 3% to
10% by weight, based on the solution mixture used.
The weight-average molecular weights M.sub.w of the polyacrylates
are situated preferably within a range from 20 000 to 2 000 000
g/mol, very preferably within a range from 100 000 to 1 000 000
g/mol, and extremely preferably in a range from 150 000 to 500 000
g/mol; the figures for the average molecular weight M.sub.w and for
the polydispersity PD in this specification relate to the
determination by gel permeation chromatography (see measurement
method A2; Experimental Section). For this purpose it may be
advantageous to carry out the polymerization in the presence of
suitable polymerization regulators such as thiols, halogen
compounds and/or alcohols, in order to set the desired average
molecular weight.
The polyacrylate preferably has a K value of 30 to 90, more
preferably of 40 to 70, as measured in toluene (1% strength
solution, 21.degree. C.). The K value according to Fikentscher is a
measure of the molecular weight and viscosity of the polymer.
Particularly suitable for the purpose of the invention are
polyacrylates which have a narrow molecular weight distribution
(polydispersity PD<4). In spite of a relatively low molecular
weight, these compositions, after crosslinking, have a particularly
good shear strength. Moreover, the lower molecular weight allows
easier processing from the melt, since the flow viscosity is lower
as compared with a broader-range polyacrylate, with largely the
same application properties. Narrow-range polyacrylates may be
prepared, advantageously, by anionic polymerization or by
controlled radical polymerization methods, the latter being
especially suitable. Examples of polyacrylates of this kind which
are prepared by the RAFT process are described in U.S. Pat. No.
6,765,078 B2 and U.S. Pat. No. 6,720,399 B2. Polyacrylates of this
kind can also be prepared via N-oxyls, as described in EP 1 311 555
B1, for example. Atom Transfer Radical Polymerization (ATRP) as
well can be employed advantageously for the synthesis of
narrow-range polyacrylates, in which case it is preferred as
initiator to use monofunctional or difunctional, secondary or
tertiary halides and, for abstracting the halide(s), complexes of
Cu, Ni, Fe, Pd, Pt, Ru, Os, Rh, Co, Ir, Ag or Au. The various
possibilities of ATRP are further described in specifications U.S.
Pat. No. 5,945,491A, U.S. Pat. No. 5,854,364 A and U.S. Pat. No.
5,789,487 A.
The polyacrylates to be crosslinked contain functional groups which
are suitable for entering into linking reactions with epoxide
groups. By linking reactions are meant, in particular, addition
reactions and substitution reactions. Preferably, then, there is a
linking of the units which carry the functional groups to the units
which carry the epoxide groups, more particularly in the sense of a
crosslinking of the polymer units which carry the functional
groups, via the epoxide-group-carrying crosslinker molecules as
linking bridges. The substances containing epoxide groups are
preferably polyfunctional epoxides, in other words those having at
least two epoxide groups; accordingly, there is overall an indirect
linking of the units which carry the functional groups.
The crosslinkable composition of the invention may comprise at
least one tackifying resin. Tackifying resins which can be used are
the existing tackifier resins described in the literature.
Reference may be made in particular to all aliphatic, aromatic and
alkylaromatic hydrocarbon resins, hydrocarbon resins based on pure
monomers, hydrogenated hydrocarbon resins, functional hydrocarbon
resins, and natural resins. With preference it is possible to use
pinene resins and indene resins, and rosins, their
disproportionated, hydrogenated, polymerized and esterified
derivatives and salts, terpene resins and terpene-phenolic resins,
and also C5 resins, C9 resins and other hydrocarbon resins.
Combinations of these and further resins may also be used with
advantage in order to adjust the properties of the resultant
composition in accordance with what is desired. With particular
preference is it possible to use all resins that are compatible
(soluble) with the polyacrylate in question. With particular
preference the crosslinkable composition of the invention comprises
terpene-phenolic resins and/or rosin esters.
The crosslinkable composition of the invention may optionally also
comprise fillers in powder and/or granular form, likewise dyes and
pigments, including more particularly abrasive and reinforcing
fillers such as, for example, chalks (CaCO.sub.3), titanium
dioxides, zinc oxides and carbon blacks, even in high proportions,
in other words from 1% to 50% by weight, based on the overall
formula. With great preference it is possible to use various forms
of chalk as a filler, with particular preference being given to the
use of Mikrosohl chalk. At preferred fractions of up to 30% by
weight, based on the overall composition, the addition of fillers
produces virtually no change in the technical adhesive properties
(shear strength at RT, instantaneous bond strength to steel and
PE).
Furthermore, fillers of low flammability, such as ammonium
polyphosphate, for example; electrically conductive fillers such as
conductive carbon black, carbon fibres and/or silver-coated beads,
for example; thermally conductive materials such as boron nitride,
aluminium oxide and silicon carbide, for example; ferromagnetic
additives such as iron(III) oxides, for example; additives for
increasing volume, more particularly for producing foamed layers or
syntactic foams, such as, for example, expandants, solid glass
beads, hollow glass beads, carbonized microbeads, hollow phenolic
microbeads and microbeads of other materials, expandable
microballoons (Expancel.RTM. from AkzoNobel), silica, silicates,
organically renewable raw materials such as wood flour, for
example, organic and/or inorganic nanoparticles, fibres; ageing
inhibitors, light stabilizers, ozone inhibitors, compounding agents
and/or expandants, may be present in the crosslinkable composition
or in the fully crosslinked composition. Ageing inhibitors which
can be used are preferably not only primary inhibitors, such as
4-methoxyphenol or Irganox.RTM. 1076, but also secondary ageing
inhibitors, such as Irgafos.RTM. TNPP or Irgafos.RTM. 168 from
BASF, optionally also in combination with one another. Other ageing
inhibitors which can be used are phenothiazine (C radical
scavenger) and also hydroquinone methyl ether in the presence of
oxygen, and also oxygen itself.
Optionally it is possible to add customary plasticizers
(plasticizing agents), more particularly in concentrations of up to
5% by weight. Plasticizers which can be metered in are, for
example, low molecular weight polyacrylates, phthalates,
water-soluble plasticizers, plasticizer resins, phosphates,
polyphosphates, adipates and/or citrates.
As a further possible option, the thermally crosslinkable and/or
crosslinked polyacrylate or polyacrylates may in accordance with
the invention also be blended with other polymers. Suitable for
this purpose are polymers based on natural rubber, synthetic
rubber, EVA, silicone rubber, acrylic rubber and polyvinyl ether.
It has proven to be useful to add these polymers in granulated or
otherwise comminuted form to the polyacrylate before the thermal
crosslinker is added. The polymer blends are produced preferably in
an extruder, more preferably in a multi-screw extruder or in a
planetary roller extruder. To stabilize the thermally crosslinked
polyacrylates, especially polymer blends of thermally crosslinked
acrylate hotmelts and other polymers, it may be sensible to
irradiate the shaped material with a low dose of electron
irradiation. For this purpose it is possible optionally to admix
the polyacrylate with crosslinking promoters such as di-, tri- or
polyfunctional acrylate, polyesters and/or urethane acrylate.
A further subject of the invention is a crosslinked polyacrylate
which is obtainable by thermal crosslinking of the thermally
crosslinkable composition of the invention.
A further subject of the invention is a process for the thermal
crosslinking of polyacrylates having functional groups which are
suitable for entering into linking reactions with epoxide groups,
said process encompassing the use of a crosslinker-accelerator
system of the invention.
The process of the invention may include a concentration of the
polyacrylate solution or dispersion resulting from the polymer
preparation procedure. Concentration of the polymer may take place
in the absence of the crosslinker and accelerator substances. It is
also possible, however, for one at most of these substances to be
added to the polymer even before concentration, in which case the
concentration takes place in the presence of this or these
substance(s).
The polymerisates are then preferably transferred to a compounder.
In special versions of the process of the invention, concentration
and compounding may take place in the same reactor.
The compounder used may in particular be an extruder. Within the
compounder, the polymerisates are present preferably in the melt,
either because they are in the melt state when they are introduced,
or by virtue of their heating in the compounder until a melt is
formed. The polymerisates are advantageously held in the melt in
the compounder by heating.
Where neither crosslinkers (epoxides) nor accelerators are present
in the polymerisate, the possible temperature in the melt is
limited by the decomposition temperature of the polymerisate. The
operational temperature within the compounder is typically between
80 to 150.degree. C., more particularly between 100 and 120.degree.
C.
The substances containing epoxide groups are added to the polymer
preferably before or with the addition of accelerator. They may be
added to the monomers even before or during the polymerization
phase, if they are sufficiently stable for that phase. With
particular preference, however, the substances containing epoxide
groups are added to the polymerisate either before addition to the
compounder or during addition to the compounder, in other words are
introduced into the compounder together with the polymerisates.
In a very preferred procedure the accelerator substances are added
to the polymerisates shortly before further processing, more
particularly before a coating or other shaping operation. The time
window for the addition prior to coating is guided in particular by
the potlife which is available, in other words the processing life
in the melt, without deleterious change to the properties of the
resultant product. With the process of the invention it was
possible to achieve potlives of several minutes up to several tens
of minutes (depending on the choice of the experimental
parameters), and so the accelerator ought to be added within this
time period prior to coating. The accelerator is advantageously
added as late as possible to the melt, but as early as necessary,
so that there is still effective homogenization with the polymer
composition.
Time periods which have emerged as being very advantageous here are
those from 2 to 10 minutes, more particularly those of more than 5
minutes, before the beginning of further processing, at an
operating temperature of 110 to 120.degree. C.
The crosslinkers (epoxides) and the accelerators can also both be
added shortly before the further processing of the polymer, in
other words advantageously in the phase as set out above for the
accelerators. For this purpose it is advantageous if crosslinkers
and accelerators are introduced into the operation simultaneously,
at the same location, possibly in the form of an
epoxide-accelerator blend.
In principle it is also possible to switch the times of addition
and/or locations of addition for crosslinker and accelerator in the
versions set out above, so that the accelerator may be added before
the substances containing epoxide groups.
In the compounding operation, the temperature of the polymerisate
on addition of the crosslinkers and/or accelerators is preferably
between 50 and 150.degree. C., more preferably between 70 and
130.degree. C. and very preferably between 80 and 120.degree.
C.
It has emerged in principle as being very advantageous for the
crosslinker, i.e. the substance containing epoxide groups, to be
added at 0.1%-5% by weight, more preferably 0.15%-0.4% by weight,
based on the polymer without additives. It is advantageous to add
the accelerator at 0.05%-5% by weight, more preferably at 0.1%-1.2%
by weight, based on the additive-free polymer. It is particularly
advantageous if the crosslinker fraction is selected so as to
result in an elastic fraction of the crosslinked polyacrylates of
at least 20%. The elastic fraction is preferably at least 40%, more
preferably at least 60% (measured in each case by measurement
method H3; cf. Experimental Section).
After coating has taken place, the polymer composition cools
relatively rapidly, down to the storage temperature, generally to
room temperature. The crosslinker-accelerator system of the
invention is outstandingly suitable for causing the crosslinking
reaction to progress without the supply of further thermal energy
(without heat supply). The inventive accelerator or accelerators
and accelerator concentrations may advantageously be selected such
that the elastic fraction of the polyacrylate after departure from
the compounding operation, at lower temperatures than in the
operation, such as at room temperature, for example, exceeds a
level of 25%, preferably of 35%, within a week, preferably within
three days, so that there is already a functional product (more
particularly an adhesive tape or a functional carrier layer based
on the polyacrylate).
The crosslinking reaction between the functional groups of the
polyacrylate and the epoxides, by means of the
crosslinker-accelerator system of the invention, thus proceeds even
without supply of heat under standard conditions, more particularly
at room temperature, to completion.
For stating the proportions of the constituents of the
crosslinker-accelerator system of the invention to one another or
to the polyacrylate to be crosslinked, it is possible to use the
ratio of the number of epoxide groups in the crosslinker to the
number of reactive functional groups in the polyacrylate. In
principle this ratio can be selected freely, with either an excess
of functional groups, numerical equality of the groups, or an
excess of epoxide groups.
This ratio is preferably selected such that the epoxide groups are
in deficit or at most in numerical equality; with very particular
preference, the ratio of the total number of epoxide groups in the
crosslinker to the number of functional groups in the polyacrylate
that are suitable for entering into linking reactions with epoxide
groups is in the range from 0.01:1 to 1:1, more particularly in the
range from 0.02:1 to 0.4:1.
Preferably, therefore, the functional groups, more preferably
carboxylic acid groups, in the polyacrylate are present in an
excess over the epoxide groups, so that the polymerisate contains a
sufficiently large number of functional groups--that is, potential
crosslinking or linking sites--in order to achieve the desired
crosslinking.
The ratio of the number of acceleration-active groups in the
accelerator to the number of epoxide groups in the crosslinker may
in principle be selected freely, so there is alternatively an
excess of acceleration-active groups, numerical equality of the
groups, or an excess of epoxide groups. Groups considered to be
acceleration-active groups are amino groups and phosphino groups,
terms which comprehend all primary, secondary and tertiary, and
hence all substituted and unsubstituted, amino and phosphino
groups. The ratio of the number of all the substituted and
unsubstituted amino and phosphino groups in the accelerator to the
number of epoxide groups in the crosslinker is preferably from
0.2:1 to 4:1.
After the composition has been compounded, the polymer can be
processed further, more particularly by coating onto a permanent or
temporary carrier. A permanent carrier remains joined to the layer
of adhesive in the application, whereas the temporary carrier is
removed in the course of further processing, as for example when
converting the adhesive tape, or at the time of application of the
layer of adhesive.
Coating of the self-adhesive compositions may take place using
hotmelt coating nozzles known to the skilled person, or,
preferably, using roll applicator mechanisms, also called coating
calenders. The coating calenders may consist advantageously of two,
three, four or more rolls.
Preferably at least one of the rolls is provided with an
anti-adhesive roll surface, this being true preferably of all of
the rolls that come into contact with the polyacrylate. In an
advantageous procedure it is possible for all of the rolls of the
calender to have an anti-adhesive finish. An anti-adhesive roll
surface used is preferably a steel-ceramic-silicone composite. Roll
surfaces of this kind are resistant to thermal and mechanical
loads.
It has emerged as being particularly advantageous if roll surfaces
are used that have a surface structure, more particularly of a kind
such that the surface does not produce full contact with the
polymer layer to be processed, but instead such that the area of
contact is lower as compared with a smooth roll. Particularly
advantageous are structured rolls such as engraved metal
rolls--engraved steel rolls, for example.
Coating may take place with particular advantage in accordance with
the coating techniques set out in WO 2006/027387 A1 from page 12,
line 5 to page 20, line 13, and more particularly as in the
sections "Variant A" (page 12), "Variant B" (page 13), "Variant C"
(page 15), "Method D" (page 17), "Variant E" (page 19) and also
FIGS. 1 to 6.
The stated disclosure passages from WO 2006/027387 A1 are therefore
explicitly included in the disclosure content of the present
specification.
When coating it is possible to realise coating speeds of up to 300
m/min, especially when using multi-roll calenders.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a compounding and coating operation in a continuous
process.
FIG. 2 is a graph depicting the effect of epoxide concentration on
the degree of crosslinking for a given amount of accelerator and a
given temperature.
FIG. 3 is a graph depicting the effect of accelerator concentration
for a given temperature (in this case room temperature) and with a
constant amount of epoxide.
FIG. 4 shows a process for making a three-layer composition by
2-roll calendar.
FIG. 5 is a graph depicting room temperature kinetics of different
accelerators with the same epoxide concentrations and the same
number of basic groups.
Shown by way of example in FIG. 1 of the present specification is
the compounding and coating operation, on the basis of a continuous
process. The polymers are introduced at the first feed point (1.1)
into the compounder (1.3), here for example an extruder. Either the
introduction takes place already in the melt, or the polymers are
heated in the compounder until the melt state is reached. At the
first feed point, together with the polymer, the epoxide-containing
compounds are advantageously introduced into the compounder.
Shortly before coating takes place, the accelerators are added at a
second feed point (1.2). The outcome of this is that the
accelerators are added to the epoxide-containing polymers not until
shortly before coating, and the reaction time in the melt is
low.
The reaction regime may also be discontinuous. In corresponding
compounders such as reactor tanks, for example, the addition of the
polymers, of the crosslinkers and of the accelerators may take
place at different times and not, as shown in FIG. 1, at different
locations.
Immediately after coating--preferably by means of roll application
or by means of an extrusion die--the polymer is only slightly
crosslinked, but not yet sufficiently crosslinked. The crosslinking
reaction preferably proceeds predominantly on the carrier.
Crosslinking raises the cohesion of the polymer and hence also the
shear strength. The links are very stable. This allows very
ageing-stable and heat-resistant products to be produced, such as
adhesive tapes, viscoelastic carrier materials or shaped
articles.
The physical properties of the end product, especially its
viscosity, bond strength and tack, can be influenced through the
degree of crosslinking, and so the end product can be optimized
through an appropriate choice of the reaction conditions. A variety
of factors determine the operational window of this process. The
most important influencing variables are the amounts
(concentrations and proportions relative to one another), the
chemical nature of the crosslinkers and the accelerators, the
operating and coating temperatures, the residence time in the
compounder (more particularly extruder) and in the coating
assembly, the fraction of functional groups, more particularly acid
groups and/or hydroxyl groups, in the polymer, and also the average
molecular weight of the polyacrylate.
The crosslinker-accelerator system of the invention, in processes
for the crosslinking of polyacrylates, offers the advantage that a
stable crosslinking process for polyacrylates can be offered, and
one with outstanding control facility in relation to the
crosslinking pattern, by virtue of substantial decoupling of degree
of crosslinking and reactivity (reaction kinetics), more
particularly the reaction kinetics at low temperatures. The amount
of crosslinker (amount of epoxide) added here largely influences
the degree of crosslinking of the product; the chemical nature and
the concentration of the accelerator largely control the
reactivity.
Surprisingly it has been observed that through the amount of
epoxide-containing substances added it has been possible to
preselect the degree of crosslinking, and to do so largely
independently of the process parameters that typically require
additional selection: temperature and amount of added
crosslinker.
The effect of epoxide group concentration on the degree of
crosslinking for a given amount of accelerator and a given
temperature is shown schematically by FIG. 2. Here, the accelerator
concentration rises from the concentration A (top curve; low
concentration) via the concentrations B (second-lowest
concentration) and C (second-highest concentration) to the
concentration D (bottom curve; highest concentration). As can be
seen, the final value of the degree of crosslinking--represented
here by increasingly smaller values for the microshear travel--goes
up as the epoxide concentration increases, whereas the reaction
kinetics remain virtually unaffected.
It has also been found that the amount of accelerator added has a
direct influence on the crosslinking rate, and hence also on the
point in time at which the final degree of crosslinking is
achieved, but without influencing it absolutely. The reactivity of
the crosslinking reaction here may be selected such that the
crosslinking also during storage of the completed product under the
conditions customary therein (room temperature) leads within a few
weeks to the desired degree of crosslinking, more particularly
without any need for thermal energy to be (actively) supplied or
for the product to be treated further.
The relationship between crosslinking time and accelerator
concentration for a given temperature (in this case room
temperature) and with a constant amount of epoxide is reproduced
schematically in FIG. 3. Here, the accelerator concentration rises
from the concentration 1 (top curve; low concentration) via the
concentrations 2 (second-lowest concentration) and 3
(second-highest concentration) to the concentration 4 (bottom
curve; highest concentration). Here it is found that the final
value of the degree of crosslinking remains virtually constant (in
the case of the lowest reaction, this value has not yet been
reached); with high concentrations of accelerator, however, this
value is reached more quickly than at low concentrations of
accelerator.
In addition to the aforementioned parameters, the reactivity of the
crosslinking reaction can also be influenced by varying the
temperature, if desired, especially in those cases where the
advantage of "inherent crosslinking" in the course of storage under
standard conditions has no part to play. At constant crosslinker
concentration, an increase in the operating temperature leads to a
reduced viscosity, which enhances the coatability of the
composition but reduces the processing life.
An increase in the processing life is acquired by a reduction in
the accelerator concentration, reduction in molecular weight,
reduction in the concentration of functional groups in the addition
polymer, reduction of the acid fraction in the addition polymer,
use of less-reactive crosslinkers (epoxides) or of less-reactive
crosslinker-accelerator systems, and reduction in operating
temperature.
An improvement in the cohesion of the composition can be obtained
by a variety of pathways. In one, the accelerator concentration is
increased, which reduces the processing life. At constant
accelerator concentration, it also possible to raise the molecular
weight of the polyacrylate, which is possibly more efficient. In
the sense of the invention it is advantageous in any case to raise
the concentration of crosslinker (substances containing epoxide
groups). Depending on the desired requirements profile of the
composition or of the product it is necessary to adapt the
abovementioned parameters in a suitable way.
A further subject of the invention is the use of a
crosslinker-accelerator system of the invention for producing
thermally crosslinked polyacrylates.
Inventively crosslinked polyacrylates can be used for a broad range
of applications. Below, a number of particularly advantageous
fields of use are set out by way of example.
A polyacrylate crosslinked with the crosslinker-accelerator system
of the invention is used in particular as a pressure-sensitive
adhesive (PSA), preferably as a PSA for an adhesive tape, where the
acrylate PSA is in the form of a single-sided or double-sided film
on a carrier sheet. These polyacrylates are especially suitable
when a high coat weight in one coat is required, since with this
coating technique it is possible to achieve an almost arbitrarily
high coat weight, preferably more than 100 g/m.sup.2, more
preferably more than 200 g/m.sup.2, and to do so in particular at
the same time as homogeneous crosslinking through the coat.
Examples of favourable applications are technical adhesive tapes,
more especially for use in construction, examples being insulating
tapes, corrosion control tapes, adhesive aluminium tapes,
fabric-reinforced film-backed adhesive tapes (duct tapes),
special-purpose adhesive construction tapes, such as vapour
barriers, adhesive assembly tapes, cable wrapping tapes,
self-adhesive sheets and/or paper labels.
The inventively crosslinked polyacrylate may also be made available
as a PSA for a carrierless adhesive tape, in the form of what is
called an adhesive transfer tape. Here as well, the possibility of
setting the coat weight almost arbitrarily high in conjunction with
homogeneous crosslinking through the coat is a particular
advantage. Preferred weights per unit area are more than 10
g/m.sup.2 to 5000 g/m.sup.2, more preferably 100 g/m.sup.2 to 3000
g/m.sup.2.
The inventively crosslinked polyacrylate may also be present in the
form of a heat-sealing adhesive in adhesive transfer tapes or
single-sided or double-sided adhesive tapes. Here as well, for
carrier-containing pressure-sensitive adhesive tapes, the carrier
may be an inventively obtained viscoelastic polyacrylate.
One advantageous embodiment of the adhesive tapes obtained using an
inventively crosslinked polyacrylate can be used as a strippable
adhesive tape, more particularly a tape which can be detached again
without residue by pulling substantially in the plane of the
bond.
The crosslinker-accelerator system of the invention or the
crosslinker composition of the invention is also particularly
suitable for producing three-dimensional shaped articles, whether
they be tacky or not. A particular advantage of this process is
that there is no restriction on the layer thickness of the
polyacrylate to be crosslinked and shaped, in contrast to UV and
EBC curing processes. In accordance with the choice of coating
assembly or shaping assembly, therefore, it is possible to produce
structures of any desired shape, which are then able to continue
crosslinking to desired strength under mild conditions.
This system or composition is also particularly suitable for the
production of particularly thick layers, especially of
pressure-sensitive adhesive layers or viscoelastic acrylate layers,
with a thickness of more than 80 .mu.m. Layers of this kind are
difficult to produce with the solvent technology, since, for
example, this technology entails bubble formation and very slow
coating speeds. The alternative lamination of thin layers one over
another is complicated and harbours weak points.
Thick pressure-sensitive adhesive layers may be present, for
example, in unfilled form, as straight acrylate, or in
resin-blended form or in a form filled with organic or inorganic
fillers. Also possible is the production of layers foamed to a
closed-cell or open-cell form in accordance with the known
techniques, as well as of syntactic foams, using the
crosslinker-accelerator system of the invention or the thermally
crosslinkable composition of the invention. Possible methods of
foaming are those of foaming via compressed gases such as nitrogen
or CO.sub.2, or foaming via expandants such as hydrazines or
expandable microballoons. Where expandable microballoons are used,
the composition or the shaped layer is advantageously activated
suitably by means of heat introduction. Foaming may take place in
the extruder or after coating. It may be judicious to smooth the
foamed layer by means of suitable rollers or release films. To
produce foam-analogous layers it is also possible to add hollow
glass beads or pre-expanded polymeric microballoons to the tacky,
thermally crosslinked polyacrylate.
In particular it is possible, using systems or compositions of the
invention, to produce thick layers as well, which can be used as a
carrier layer for double-sidedly PSA-coated adhesive tapes. With
particular preference these are filled and foamed layers which can
be utilized as carrier layers for foamlike adhesive tapes. With
these layers as well it is sensible to add hollow glass beads,
solid glass beads or expanding microballoons to the polyacrylate
prior to the addition of the crosslinker-accelerator system or of
the crosslinker or of the accelerator. It is possible to laminate a
pressure-sensitive adhesive layer onto at least one side of a
foamlike viscoelastic layer of this kind. It is preferred to
laminate a corona-pretreated polyacrylate layer on both sides.
Alternatively it is possible to laminate differently pretreated
adhesive layers, i.e. pressure-sensitive adhesive layers and/or
heat-activable layers based on polymers other than on acrylates,
onto the viscoelastic layer. Suitable base polymers are adhesives
based on natural rubber, synthetic rubbers, acrylate block
copolymers, styrene block copolymers, EVA, certain polyolefins,
specific polyurethanes, polyvinyl ethers, and silicones. Preferred
compositions, however, are those which have no significant fraction
of migratable constituents and whose compatibility with the
polyacrylate is so good that they diffuse in significant quantities
into the acrylate layer and alter the properties therein.
Instead of laminating a pressure-sensitive adhesive layer onto both
sides, it is also possible on at least one side to use a
hotmelt-adhesive layer or thermally activable adhesive layer.
Asymmetric adhesive tapes of this kind allow the bonding of
critical substrates with a high bonding strength. An adhesive tape
of this kind can be used, for example, to affix EPDM rubber
profiles to vehicles.
One particular advantage of the inventively crosslinked
polyacrylates is that these layers, whether utilized as a
viscoelastic carrier, as a pressure-sensitive adhesive or as a
heat-sealing composition, combine an equal surface quality with no
crosslinking profile through the layer (or, correspondingly,
through the shaped article produced from the polyacrylates)--in
particular in contrast to UV-crosslinked and EBC-crosslinked
layers. As a result it is possible for the balance between adhesive
and cohesive properties to be controlled and set ideally for the
layer as a whole through the crosslinking. In the case of
radiation-crosslinked layers, in contrast, there is generally one
side or one sublayer which is over- or undercrosslinked.
EXAMPLES
Measurement Methods (General):
K Value (According to Fikentscher) (Measurement Method A1):
The K value is a measure of the average molecular size of
high-polymer materials. It is measured by preparing one percent
strength (1 g/100 ml) toluenic polymer solutions and determining
their kinematic viscosities using a Vogel-Ossag viscometer.
Standardization to the viscosity of the toluene gives the relative
viscosity, from which the K value can be calculated by the method
of Fikentscher (Polymer 1967, 8, 381 ff.)
Gel Permeation Chromatography GPC (Measurement Method A2):
The figures for the weight-average molecular weight M.sub.w and the
polydispersity PD in this specification relate to the determination
by gel permeation chromatography. Determination is made on a 100
.mu.l sample subjected to clarifying filtration (sample
concentration 4 g/l). The eluent used is tetrahydrofuran with 0.1%
by volume of trifluoroacetic acid. Measurement takes place at
25.degree. C. The preliminary column used is a column type PSS-SDV,
5.mu., 10.sup.3 .ANG., ID 8.0 mm 50 mm. Separation is carried out
using the columns of type PSS-SDV, 5.mu., 10.sup.3 .ANG. and also
10.sup.5 .ANG. and 10.sup.6 .ANG. each with ID 8.0 mm.times.300 mm
(columns from Polymer Standards Service; detection by means of
Shodex R171 differential refractometer). The flow rate is 1.0 ml
per minute. Calibration takes place against PMMA standards
(polymethyl methacrylate calibration).
Solids Content (Measurement Method A3):
The solids content is a measure of the fraction of non-evaporable
constituents in a polymer solution. It is determined
gravimetrically, by weighing the solution, then evaporating the
evaporable fractions in a drying cabinet at 120.degree. C. for 2
hours and reweighing the residue.
Measurement Methods (PSAs):
180.degree. Bond Strength Test (Measurement Method H1):
A strip 20 mm wide of an acrylate PSA applied to polyester as a
layer was applied to steel plates which beforehand had been washed
twice with acetone and once with isopropanol. The
pressure-sensitive adhesive strip was pressed onto the substrate
twice with an applied pressure corresponding to a weight of 2 kg.
The adhesive tape was then removed from the substrate immediately
with a speed of 300 mm/min and at an angle of 180.degree.. All
measurements were conducted at room temperature.
The results are reported in N/cm and have been averaged from three
measurements. The bond strength to polyethylene (PE) was determined
analogously.
Holding Power (Measurement Method H2):
A strip of the adhesive tape 13 mm wide and more than 20 mm long
(30 mm, for example) was applied to a smooth steel surface which
had been cleaned three times with acetone and once with
isopropanol. The bond area was 20 mm13 mm (lengthwidth), the
adhesive tape protruding beyond the test plate at the edge (by 10
mm, for example, corresponding to aforementioned length of 30 mm).
Subsequently the adhesive tape was pressed onto the steel support
four times, with an applied pressure corresponding to a weight of 2
kg. This sample was suspended vertically, with the protruding end
of the adhesive tape pointing downwards.
At room temperature, a weight of 1 kg was affixed to the protruding
end of the adhesive tape. Measurement is conducted under standard
conditions (23.degree. C., 55% humidity) and at 70.degree. C. in a
thermal cabinet.
The holding power times measured (times taken for the adhesive tape
to detach completely from the substrate; measurement terminated at
10 000 min) are reported in minutes and correspond to the average
value from three measurements.
Microshear Test (Measurement Method H3):
This test serves for the accelerated testing of the shear strength
of adhesive tapes under temperature load.
Sample Preparation for Microshear Test:
An adhesive tape (length about 50 mm, width 10 mm) cut from the
respective sample specimen is adhered to a steel test plate, which
has been cleaned with acetone, in such a way that the steel plate
protrudes beyond the adhesive tape to the right and the left, and
that the adhesive tape protrudes beyond the test plate by 2 mm at
the top edge. The bond area of the sample in terms of
heightwidth=13 mm10 mm. The bond site is subsequently rolled over
six times with a 2 kg steel roller at a speed of 10 m/min. The
adhesive tape is reinforced flush with a stable adhesive strip
which serves as a support for the travel sensor. The sample is
suspended vertically by means of the test plate.
Microshear Test:
The sample specimen for measurement is loaded at the bottom end
with a weight of 100 g. The test temperature is 40.degree. C., the
test duration 30 minutes (15 minutes' loading and 15 minutes'
unloading). The shear travel after the predetermined test duration
at constant temperature is reported as the result in .mu.m, as both
the maximum value ["max"; maximum shear travel as a result of
15-minute loading]; and the minimum value ["min"; shear travel
("residual deflection") 15 minutes after unloading; on unloading
there is a backward movement as a result of relaxation]. Likewise
reported is the elastic component in percent ["elast"; elastic
fraction=(max-min)100/max].
Measurement Methods (Three-Layer Constructions):
90.degree. Bond Strength to Steel--Open and Lined Side (Measurement
Method V1):
The bond strength to steel is determined under test conditions of
23.degree. C.+/-1.degree. C. temperature and 50%+/-5% relative
humidity. The specimens were cut to a width of 20 mm and adhered to
a steel plate. Prior to the measurement the steel plate is cleaned
and conditioned. For this purpose the plate is first wiped down
with acetone and then left to stand in the air for 5 minutes to
allow the solvent to evaporate. The side of the three-layer
assembly facing away from the test substrate was then lined with a
50 .mu.m aluminium foil, thereby preventing the sample from
expanding in the course of the measurement. This was followed by
the rolling of the test specimen onto the steel substrate. For this
purpose the tape was rolled over 5 times back and forth with a
rolling speed of 10 m/min using a 2 kg roller. Immediately after
the rolling-on operation, the steel plate was inserted into a
special mount which allows the specimen to be removed at an angle
of 90.degree. vertically upwards. The measurement of bond strength
was made using a Zwick tensile testing machine. When the lined side
is applied to the steel plate, the open side of the three-layer
assembly is first laminated to the 50 .mu.m aluminium foil, the
release material is removed, and the system is adhered to the steel
plate, and subjected to analogous rolling-on and measurement.
The results measured on both sides, open and lined, are reported in
N/cm and are averaged from three measurements.
Holding Power--Open and Lined Side (Measurement Method V2):
Specimen preparation took place under test conditions of 23.degree.
C.+/-1.degree. C. temperature and 50%+/-5% relative humidity. The
test specimen was cut to 13 mm and adhered to a steel plate. The
bond area is 20 mm13 mm (lengthwidth). Prior to the measurement,
the steel plate was cleaned and conditioned. For this purpose the
plate was first wiped down with acetone and then left to stand in
the air for 5 minutes to allow the solvent to evaporate. After
bonding had taken place, the open side was reinforced with a 50
.mu.m aluminium foil and rolled over back and forth 2 times using a
2 kg roller. Subsequently a belt loop was attached to the
protruding end of the three-layer assembly. The whole system was
then suspended from a suitable device and subjected to a load of 10
N. The suspension device is such that the weight loads the sample
at an angle of 179.degree..+-./-1.degree.. This ensures that the
three-layer assembly is unable to peel from the bottom edge of the
plate. The measured holding power, the time between suspension and
dropping of the sample, is reported in minutes and corresponds to
the average value from three measurements. To measure the lined
side, the open side is first reinforced with the 50 .mu.m aluminium
foil, the release material is removed, and adhesion to the test
plate takes place as described. The measurement is conducted under
standard conditions (23.degree. C., 55% humidity).
Commercially Available Chemicals Used
TABLE-US-00001 Chemical compound Trade name Manufacturer CAS No.
2,2'-Azobis(2-methylbutyronitrile) Vazo .RTM. 67 DuPont 13472-08-7
2,2'-Azobis(isobutyronitrile), AIBN Vazo .RTM. 64 DuPont 78-67-1
Bis-(4-tert-butylcyclohexyl)peroxydicarbonate Perkadox .RTM. 16
Akzo Nobel 15520-11-3 Terpene-phenolic-based tackifier Dertophene
.RTM. T105 DRT, France 73597-48-5 resin (softening point
105.degree. C., hydroxyl value 30-60) Pentaerythritol tetraglycidyl
ether Polypox .RTM. R16 UPPC AG 3126-63-4 3,4-Epoxycyclohexylmethyl
3,4- Uvacure .RTM. 1500 Cytec Industries 2386-87-0
epoxycyclohexanecarboxylate Inc. Dimethyl propanephosphonate
Levagard .RTM. DMPP Lanxess 18755-43-6 N,N,N,N,N-Pentamethyl-
Jeffcat .RTM. ZR-40 Huntsman 3030-47-5 diethylenetriamine
N'-(3-(Dimethylamino)propyl)-N,N- Jeffcat .RTM. Z-130 Huntsman
6711-48-4 dimethyl-1,3-propanediamine Diethylenetriamine Epikare
.RTM. 3223 Hexion Spec. 111-40-0 Chemicals N,N,N,N-Tetramethyl-
Sigma-Aldrich 51-80-9 methanediamine Thermoplastic hollow
microbeads Expancel .RTM. 092 DU Akzo Nobel (particle size 10-17
.mu.m; density max. 40 0.017 g/cm.sup.3; expansion temperature
127-139.degree. C. [start]; 164-184.degree. C. [max. exp.]) all
specification figures at 20.degree. C.; Epikare .RTM. also sold
under the Epi-Cure .RTM. and Bakelite .RTM. EPH trade names
Pressure Sensitive Adhesive (PSA) Examples Preparation of Starting
Polymers for Examples B1 to B4
Described below is the preparation of the starting polymers. The
polymers investigated are prepared conventionally via free radical
polymerization in solution.
Base Polymer P1
A reactor conventional for free-radical polymerizations was charged
with 30 kg of 2-ethylhexyl acrylate, 67 kg of n-butyl acrylate, 3
kg of acrylic acid, and 66 kg of acetone/isopropanol (96:4). After
nitrogen gas had been passed through the reactor for 45 minutes
with stirring, the reactor was heated to 58.degree. C. and 50 g of
2,2'-azobis(2-methylbutyronitrile) were added. Subsequently the
external heating bath was heated to 75.degree. C. and the reaction
was carried out constantly at this external temperature. After 1 h
a further 50 g of 2,2'-azobis(2-methylbutyronitrile) were added,
and after 4 h the batch was diluted with 23 kg of
acetone/isopropanol mixture (96:4).
After 5 h and again after 7 h, reinitiation took place with 150 g
of bis(4-tert-butylcyclohexyl) peroxydicarbonate in each case.
After a reaction time of 22 h the polymerization was terminated and
the batch was cooled to room temperature. The polyacrylate has a
conversion of 99.6%, a K value of 75.1, an average molecular weight
of M.sub.w=1 480 000 g/mol, polydispersity PD
(M.sub.w/M.sub.n)=16.1.
Base Polymer P2 (Viscoelastic Carrier)
In the same way as in Example P1, 68 kg of 2-ethylhexyl acrylate,
25 kg of methyl acrylate and 7 kg of acrylic acid were polymerized
in 66 kg of acetone/isopropanol (94:6). Initiation was carried out
twice with 50 g of 2,2-azobis(2-methylbutyronitrile) in each case,
twice with 150 g of bis(4-tert-butylcyclohexyl) peroxydicarbonate
in each case, and dilution was carried out with 20 kg of
acetone/isopropanol mixture (94:6). After a reaction time of 22 h
the polymerization was terminated and the batch was cooled to room
temperature.
The polyacrylate has a conversion of 99.7%, a K value of 51.3 and
an average molecular weight of M.sub.w=676 000 g/mol,
polydispersity PD (M.sub.w/M.sub.n)=9.5.
Base Polymer P3 (PSA for Three-Layer Construction in Combination
with Viscoelastic Carrier)
In the same way as in Example P1, 24.0 kg of 2-ethylhexyl acrylate,
12.0 kg of n-butyl acrylate and 4.0 kg of acrylic acid were
polymerized in 26.7 kg of acetone/benzine 60/95 (1:1). After
nitrogen gas had been passed through the reactor for 45 minutes
with stirring, the reactor was heated to 58.degree. C. and 30 g of
AIBN were added. The external heating bath was subsequently heated
to 75.degree. C. and the reaction was carried out constantly at
this external temperature. After a reaction time of 1 h, a further
30 g of AIBN were added. After 4 h and 8 h, dilution took place
with 10.0 kg each time of an acetone/benzene 60/95 (1:1) mixture.
For reduction of the residual initiators, 90 g portions of
bis-(4-tert-butylcyclohexyl) peroxydicarbonate were added after 8 h
and again after 10 h. After a reaction time of 24 h, the reaction
was terminated and the batch was cooled to room temperature.
The polyacrylate has a conversion of 99.7%, a K value of 46.9 and
an average molecular weight of M.sub.w=1 500 900 g/mol,
polydispersity PD (M.sub.w/M.sub.n)=17.0.
Process 1: Concentration/Preparation of the Hotmelt PSAs:
The acrylate copolymers (base polymers P1 and P2) are very largely
freed from the solvent by means of a single-screw extruder
(concentrating extruder, Berstorff GmbH, Germany) (residual solvent
content .ltoreq.0.3% by weight; cf. the individual examples). The
parameters given here by way of example are those for the
concentration of base polymer P1. The screw speed was 150 rpm, the
motor current 15 A, and a throughput of 58.0 kg liquid/h was
realized. For concentration, a vacuum was applied at 3 different
domes. The reduced pressures were, respectively, between 20 mbar
and 300 mbar. The exit temperature of the concentrated hotmelt is
approximately 115.degree. C. The solids content after this
concentration step was 99.8%.
Process 2: Preparation of the Modified Hotmelt PSAs and
Viscoelastic Carriers:
The acrylate hotmelt PSAs prepared in accordance with Process 1 as
elucidated above were conveyed directly into a downstream Welding
twin-screw extruder (Welding Engineers, Orlando, USA; model 30 mm
DWD; screw diameter 30 mm, length of screw 1=1258 mm; length of
screw 2=1081 mm; 3 zones). Via a solids metering system, the resin
Dertophene.RTM. T105 was metered in zone 1 and mixed in
homogeneously. In the case of the composition for Examples MT 1, no
resin was metered in; instead, the hollow thermoplastic microbeads,
mixed to a paste with Levagard.RTM. DMPP beforehand, were metered
in via the solids metering system. The parameters given here by way
of example are those for resin compounding with base polymer P1.
The speed was 451 rpm, the motor current 42 A, and a throughput of
30.1 kg/h was realized. The temperatures of zones 1 and 2 were each
105.degree. C., the melt temperature in zone 1 was 117.degree. C.,
and the composition temperature on exit (zone 3) was 100.degree.
C.
Process 3: Production of the Inventive Adhesive Tapes, Blending
with the Crosslinker-Accelerator System for Thermal Crosslinking,
and Coating:
The acrylate hotmelt PSAs prepared by Processes 1-2 were melted in
a feeder extruder (single-screw conveying extruder from Troester
GmbH & Co. KG, Germany) and using this extruder were conveyed
as a polymer melt into a twin-screw extruder (Leistritz, Germany,
ref. LSM 30/34). The assembly is heated electrically from the
outside and is air-cooled by a number of fans, and is designed such
that, with effective distribution of the crosslinker-accelerator
system in the polymer matrix, there is at the same time a short
residence time ensured for the adhesive in the extruder. For this
purpose the mixing shafts of the twin-screw extruder were arranged
in such a way that conveying elements are in alternation with
mixing elements. The addition of the respective crosslinkers and
accelerators is made with suitable metering equipment, where
appropriate at two or more points (FIG. 1: metering points 1.1 and
1.2) and, where appropriate, with the use of metering assistants
into the unpressurized conveying zones of the twin-screw extruder.
Following exit of the ready-compounded adhesive, i.e. of the
adhesive blended with the crosslinker-accelerator system, from the
twin-screw extruder (exit: circular die, 5 mm diameter), coating
takes place in accordance with FIG. 1 onto a carrier material in
web form.
The time between metered addition of the crosslinker-accelerator
system and the shaping or coating procedure is termed the
processing life. The processing life indicates the period within
which the adhesive, blended with the crosslinker-accelerator
system, or the viscoelastic carrier layer, can be coated with a
visually good appearance (gel-free, speck-free). Coating takes
place with web speeds between 1 m/min and 20 m/min; the doctor roll
of the 2-roll applicator is not driven.
In the examples and tables below, the formulations employed, the
production parameters and the properties obtained are each
described in more detail.
Process 4: Preparation of the Modified Hotmelt PSAs and
Viscoelastic Carriers:
The base polymer P3 was blended with 0.2% by weight of Uvacure.RTM.
1500, based on the polymer, then diluted with acetone to a solids
content of 30% and subsequently coated from solution onto a
siliconized release film (50 .mu.m polyester) and onto a 23 .mu.m
etched PET film (coating speed of 2.5 m/min, drying tunnel 15 m,
temperatures: Zone 1: 40.degree. C., Zone 2: 70.degree. C., Zone 3:
95.degree. C., Zone 4: 105.degree. C.). The coat weight was 50
g/m.sup.2.
Examples B1 to B4
The base polymer P1 was polymerized in accordance with the
polymerization process described, concentrated in accordance with
Process 1 (solids content 99.8%) and then blended with the
Dertophene.RTM. T105 resin in accordance with Process 2. These
resin-modified acrylate hotmelt compositions were then compounded
in accordance with Process 3 continuously with the
crosslinker-accelerator system consisting of a pentaerythrityl
tetraglycidyl ether, here Polypox.RTM. R16 from UPPC AG (epoxide)
and the respective accelerator.
Detailed description: In the twin-screw extruder described in
Process 3, a total mass flow consisting of 70 parts of polymer P1
and 30 parts each time of Dertophene.RTM. T105 resin of 533.3 g/min
(corresponding to 373 grams of the pure polymer per minute) was
blended with 0.70 g/min of the epoxide crosslinker pentaerythritol
tetraglycidyl ether (corresponding to 0.19% by weight based on
polymer) and with a predetermined amount of accelerator. The amount
of accelerator was selected such that the number of activating
basic groups is constant (see Table 1). Because of varying numbers
of functionalities per molecule, there is thus a variation in the
molar concentration of the accelerator based on the polymer.
The epoxide was metered via a peristaltic pump at metering point
1.1, and the amine was metered separately via a peristaltic pump at
metering pump 1.2 (see FIG. 1). To improve meterability and the
quality of mixing achievable, the crosslinker system used was
diluted with the liquid dimethyl propylphosphonate Levagard.RTM.
DMPP from Lanxess (ratio of the crosslinker 0.5:1). The operational
parameters are summarized in Table 2.
The processing life of the completed compounded formulations was
more than 7 minutes with an average composition temperature of
125.degree. C. after departure from the Leistritz twin-screw
extruder. Coating took place on a 2-roll applicator in accordance
with FIG. 1, at roll surface temperatures of 100.degree. C. in each
case. The coat weight in each case was 50 g/m.sup.2 on 23 .mu.m PET
film. On the adhesive tapes thus produced, measurements were made
of the bond strength to steel at room temperature and microshear
travel at 40.degree. C. as a function of the storage time (selected
example are shown in FIG. 5). The technical adhesive data of
Examples B1 to B4 are summarized in Table 3. These examples show
that very high-performance adhesive tapes can be produced,
featuring, among other qualities, high bond strengths to polar and
apolar substrates (steel and polyethylene) and good cohesive
properties even under the influence of temperature.
TABLE-US-00002 TABLE 1 Accelerator concentrations Amine
Concentration groups/100 g Example Accelerator [%] polymer [mol]
Example B1 N,N,N,N,N- 0.75 1.2 (inventive) pentamethyldiethylene-
triamine Example B2 N'-(3- 0.7 1.2 (inventive)
(dimethylamino)propyl)- N,N-dimethyl- 1,3- propanediamine
Comparative diethylenetriamine 0.41 1.2 example B3 Comparative
N,N,N,N- 0.61 1.2 example B4 tetramethylmethane diamine
When the crosslinker-accelerator system of the invention is used,
the crosslinking reaction proceeds to completion via the functional
groups of the polyacrylate, even without supply of heat, under
standard conditions (room temperature). Generally speaking, after a
storage time of 7 days to 14 days, the crosslinking reaction has
concluded to an extent such that an adhesive tape or carrier layer
present is functional. The ultimate crosslinking state and hence
the ultimate cohesion of the composition are achieved, depending on
the choice of the composition/crosslinker system, after a storage
time of 14 to 30 days, in advantageous form after 14 to 21 days'
storage time at room temperature, expected to be earlier in the
case of a higher storage temperature.
As a result of the crosslinking there is an increase in the
cohesion of the adhesive and hence also in the shear strength. The
linking groups obtained are very stable. This allows very
ageing-stable and heat-resistant self-adhesive tapes. It can be
shown, moreover, that the choice of accelerator barely influences
the adhesive properties, but very strongly influences the room
temperature kinetics (see FIG. 5 and Table 3). Consideration of
Comparative Examples B3 and B4 shows that the crosslinking is not
yet complete within the abovementioned period, or that gelation
occurs beforehand in the process unless the inventive
accelerator-crosslinker system is used.
Examples: Viscoelastic Carriers and Three-Layer Constructions
Process 5: Production of the 3-Layer Constructions by 2-Roll
Calender:
The base polymer P2 was freed in the same way as in Process 1 from
the solvents, and then optionally was admixed with additives in the
same way as in Process 2. Thereafter the process was carried out as
described in FIG. 4. Using a distributor nozzle (1), the
viscoelastic composition (3), already compounded with the
crosslinker-accelerator system and with fillers where appropriate,
is supplied to the roll nip. The shaping of the viscoelastic
composition to a viscoelastic film takes place between the calender
rolls (W1) and (W2) in the roll nip between two self-adhesive
compositions (6a, 6b), which in turn are supplied in a form where
they are coated on anti-adhesively furnished carrier materials (5a,
5b). At the same time, the viscoelastic composition is shaped to
the set layer thickness, and is coated with the two self-adhesive
compositions supplied. In order to improve the anchoring of the
self-adhesive compositions (6a, 6b) on the shaped, viscoelastic
carrier layer (4), the self-adhesive compositions are
corona-treated by corona station (8) (corona unit from Vitaphone,
Denmark, 100 Wmin/m.sup.2) before being supplied to the roll nip.
After the three-layer assembly has been produced, this treatment
leads to improved chemical attachment to the viscoelastic carrier
layer.
The web speed when travelling through the coating unit is 30
m/min.
Following departure from the roll nip, any anti-adhesive carrier
(5a) is removed, and the completed three-layer product (9) is wound
up with the remaining, second anti-adhesive carrier (5b).
Specific examples for the production of the self-adhesive
compositions and the coating of the inventive adhesive tapes are
presented below.
Examples MT1 to MT2
The base polymer P2 was concentrated by Process 1 (solids content
99.7%) and then compounded by Process 3 in a twin-screw extruder
continuously with
MT1: the crosslinker-accelerator system consisting of
pentaerythritol tetraglycidyl ether (Polypox.RTM. R 16; 0.14% by
weight based on the polyacrylate) and
N'-(3-(dimethylamino)propyl)-N,N-dimethyl-1,3-propanediamine
(Jeffcat.RTM. Z-130; 0.14% by weight based on the polyacrylate);
MT2: the crosslinker-accelerator system consisting of
pentaerythritol tetraglycidyl ether (Polypox.RTM. R 16; 0.14% by
weight based on the polyacrylate),
N'-(3-(dimethylamino)propyl)-N,N-dimethyl-1,3-propanediamine
(Jeffcat.RTM. Z-130; 0.14% by weight based on the polyacrylate) and
also Expancel.RTM. 051 DU 40 (expandable hollow thermoplastic
microbeads, 0.70% by weight based on the polymer).
Coating to produce the viscoelastic carriers VT1 and VT2 from the
base polymer P2 between the composition layers P3, coated
beforehand according to Process 4 onto siliconized polyester films,
takes place on a 2-roll applicator at roll temperatures of
100.degree. C. by Process 5. The layer thicknesses of the
viscoelastic carriers VT1 and VT2 was 800 .mu.m. The corona power
was 100 Wmin/m.sup.2. After 7 days of room-temperature storage, the
technical adhesive data were measured for both the open side and
the lined side. The data of Examples MT1 and MT2 is summarized in
Table 4.
As can be seen from the data in Table 4, the double-sided adhesive
assembly tapes of the invention have very good technical adhesive
data. Particularly positive is the balanced adhesive profile of the
respective sides. With the same layer of adhesive on both sides of
the adhesive tape, these sides exhibit virtually the same technical
adhesive data. This shows the homogeneous crosslinking through the
layer. Moreover, these three-layer adhesive tapes do not exhibit
any delamination. By virtue of the corona treatment of the
pressure-sensitive adhesive layers and of the secondary
crosslinking of the adjacent viscoelastic carrier layer, the
anchoring of the layers to one another is very good.
TABLE-US-00003 TABLE 2 Process parameters Process parameters Total
mass Target current TSE Melt temp. Base polymer Compounding as per
through- TSE consumption outlet after Doctor Coating Process- K
process 2 put in TSE speed of TSE pressure TSE roll roll ing time
Example Polymer value Fraction of adjuvants [kg/h] [1/min] [A]
[bar] [.degree. C.] DR CR [min] B1-B4 P3 75.1 70 parts polymer P3 +
32.0 110 15 12 125 100 100 greater 30 parts DT 105 resin than 7 TSE
= Twin-screw extruder; DT 105 = Dertophene .RTM. T105
TABLE-US-00004 TABLE 3 Adhesive results Adhesive properties after
storage of the specimens at room temperature for 25 days Bond Bond
Holding Holding MSW 40.degree. C./ Base polymer Coat- strength
strength power 10N, power 10N, elast. K Compounding process 2
Carrier weight to steel to PE 23.degree. C. 70.degree. C. fraction
Example Polymer value Fraction of adjuvants film [g/m.sup.2] [N/cm]
[N/cm] [min] [min] [.mu.m]/[%] B1 P3 75.1 68 parts polymer P3 + 23
.mu.m 50 8.5 3.8 1.118 95 563/64 32 parts DT 105 resin PET sheet B2
P3 75.1 68 parts polymer P3 + 23 .mu.m 50 7.9 4.2 1.437 105 491/60
32 parts DT 105 resin PET sheet B3 P3 75.1 68 parts polymer P3 + 23
.mu.m 50 Tests not possible, -- (comp.) 32 parts DT 105 resin PET
formulation has gelated sheet B4 P3 75.1 68 parts polymer P3 + 23
.mu.m 50 Tests not possible, greater than (comp.) 32 parts DT 105
resin PET formulation has not crosslinked 2000/0 sheet Bond
strength steel/PE = measurement method H1 Holding power =
measurement method H2 MST = Microshear travel = measurement method
H3 DT 105 = Dertophene .RTM. T105 For the accelerator type see
Table 2
TABLE-US-00005 TABLE 4 Product construction and technical adhesive
data for the three-layer constructions Bond strength to steel
Holding power Three-layer product Carrier [N/cm] 10N 23.degree. C.
[min] Viscoelastic thickness open lined open lined Density Example
PSA 1 carrier layer PSA 2 [.mu.m] side side side side [g/cm.sup.3]
MT1 50 g/m.sup.2 VT 1 50 g/m.sup.2 800 24.2 23.7 >10 000 >10
000 1.08 P2 P3 MT2 50 g/m.sup.2 VT 2 50 g/m.sup.2 800 35.2 34.6
.sup. 7850 .sup. 6970 0.78 P2 P3 Bond strength to steel =
measurement method V1 Holding power = measurement method V2
* * * * *